The devil is in the details, as they say. As the SARS-CoV-2 pandemic declines in the Northern hemisphere and lockdowns ease in Europe, early identification of new cases and contact tracing become paramount to tackle new expected outbreaks. Resources, personnel, infrastructures, technology and extensive social debate are needed, but also awareness on the wide variety of mild symptoms of covid-19.

So far media and scientific research have focused on the clinical characteristics of those admitted to hospital and severely ill patients, on intensive care management, and on complications leading to death. However, information remains scarce on the clinical features of people with mild or moderate symptoms. Growing evidence shows that undocumented infections and transmission from asymptomatic, pre symptomatic, or mildly symptomatic patients are responsible for the rapid spread of the disease.

Still most people consider that this infection involves what have broadly been defined as the “typical symptoms” of a respiratory disease: fever, cough, and shortness of breath. Moreover, many still think that if they don’t have fever or cough, that it could not be covid-19. 

Recent research found that only a third of 5,700 patients hospitalized for this disease in the New York metropolitan area had fever upon admission, which doesn’t seem particularly high for a symptom to be considered “typical.” We also know now that although SARS-CoV-2 is transmitted through respiratory secretions and produces severe pneumonia, covid-19 is a systemic disease that affects most body systems and can express itself in multiple ways.

As I mentioned in a previous opinion piece, in Spain’s primary care sector, family physicians, paediatricians and nurses are mostly doing phone follow up of patients isolating at home with mild symptoms. In Madrid, our country’s epicentre, we’ve noticed the strikingly broad spectrum of such manifestations.

Gastrointestinal symptoms such as diarrhoea, anorexia, and nausea are frequent complaints, as has also been described for patients admitted to hospital. They are particularly frequent in children, who usually suffer a less aggressive clinical course and have less cough, fever, or shortness of breath compared with adults. But a wide range of symptoms is also possible, including an unusual severe pediatric multisystem inflammatory syndrome.

For both adults and children, we have seen several other symptoms such as sore throat, rhinorrhoea, nasal congestion, sputum production, thorax oppression, weakness, malaise, myalgia, back pain, confusion, dizziness, headache, abdominal pain, vomits, chills, or conjunctivitis. Such variety is unlikely to be explained by coinfection with other viruses,  which has been found to be very low (2.1%).

Since mid-March anosmia, hyposmia, and dysgeusia have begun to be consistently noticed as particularly related to covid-19, sometimes as the only present symptom. 

In Madrid we have also noticed a wide variety in the intensity of symptoms and combinations, something particularly noticeable while broad widespread transmission was taking place under lockdown and most people were only seeing household contacts.

While the NHS has only added changes to smell or taste to the original list of suspicious symptoms, some more have been recently included by the CDC or the Spanish Minister of Health. However, unawareness of this diversity remains widespread.

As lockdowns are eased in Spain, citizens are told to remain home if symptomatic. But while Madrid, Catalonia, and other regions still lack proper contact tracing programs, I am concerned that such unawareness might also contribute to the a second wave.

Until we have a better understanding of these clinical presentations, covid-19 should be suspected if the previously mentioned symptoms appear, as well as characteristic conditions, such as sudden loss of smell or taste. If tests are not available and symptoms remain mild, self-isolation should be encouraged and facilitated by local authorities, particularly for those most vulnerable to the disease.

As further knowledge becomes available, our growing concern about the severe manifestations affecting multiple organs must also focus on mild symptoms. Because that’s where the devil seems to be hiding.

Aser García Rada is a paediatrician who works at a primary care center in Madrid. Twitter: @AserGRada 

Competing interests: None declared